IIBUA, please don't be too concerned. If the facts are exactly as you have reported them, and nothing else relevant is missing from your report, then you were authorised to travel on the understanding that you would buy your ticket at a later point in your journey (which includes the destination station). There was no 'entrapment'. There is no Criminal Offence. There is no 'fine' to be paid, just the fare for the journey which seems is still due to be paid.
The complications are in how and when you respond to the simple request for further information, and I have a few points to make about this:-
- If it is a regular / daily journey, is there any chance you can chat to the member of platform staff who gave you the instruction to travel tomorrow and thank them for their help, and ask if they could assist you further by confirming their instruction to the Revenue Investigations team when asked, and giving you their name for the record?
- the Officer who questioned you at the destination will have submitted a report to the Revenue Investigations team, and there is a possibility that they had positioned themselves to intercept people who were attempting to leave the station rather than to make their way to the nearest ticket seller. You will have to be clear in your own mind about that - if you were unambigously headed for the nearest ticket selling office or machine, then that is a matter of fact which absolves you of blame.
You will be asked to explain the circumstances, and that is not something to be worried about, but you do need to have the facts available to you to confirm the details, and those should be easier to obtain now, rather than a few months down the line when the question is asked.
However, if your report on here has picked out elements which support your innocence but in fact you were demonstrably hoping to escape without payment, then, there is little point in asking the platform staff for assistance, and every good reason to fear that you will be required to provide an explanation for your apparent Criminal activity - only you, and the Railway Investigator will know which scenario is true!
To respomd to some of the replies from other on here (and repeating my comments above):-
The previous Penalty Fare is of no consequence.
Railway staff are perfectly entitled to 'wave passengers through' where there is an acknowledged agreement to pay.
There was no 'entrapment'.
There is no Criminal Offence *.
There is no 'fine' to be paid *.
[* unless there are other relevant facts]